The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Low dynamic range pictures (LDR pictures) are pictures whose luminance values are represented with a limited number of bits (most often 8, 10 or 12 bits). This limited representation does not allow to correctly restitute small signal variations, in particular in dark and bright luminance's ranges. In HDR (High Dynamic Range) pictures, the signal representation is extended in order to keep a high accuracy of the signal on its entire range. In HDR pictures, pixels' value are usually represented in floating-point format (either 32-bit or 16-bit for each component), the most popular format being openEXR half-float format (16-bit per RGB component, i.e. 48 bits per pixel). Without compression, the size of a HDR picture in HD format (1920×1080 pixels) in openEXR half-float format is 99 532 800 bits. Considering a video at 25 fps, this approximately leads to a data rate of 2.488 Gbps. Since 7 Mbps is a typical data rate used for broadcast distribution, there is a need to compress and encode these HDR pictures.
Today, the majority of HDR encoding methods based on legacy encoders such as MPEG encoders requires the use of at least one professional encoder able to encode 12 or 14 bits content. Such professional encoders are expensive. In addition to the professional encoder, some of these methods use a 8 bit encoder for encoding a LDR version of the HDR pictures. The LDR picture is usually a tone mapped version of the HDR picture. Tone mapping is known to introduce artifacts.
Dual modulation methods are usually used in the dual modulation HDR displays. Such dual modulation HDR displays are made of two panels:                one LED panel as a backlight panel that generates low resolution luminance picture of the scene; and        one LCD panel that modulates the light coming from the LED panel to generate the resulting HDR picture.In order to feed these two panels, a HDR picture is first decomposed in two separate LDR pictures, one picture is for the LED panel and the other one is for the LCD panel. Dual modulation methods are designed to deliver pictures with light levels that correspond to the value of the HDR input content, i.e. HDR input pictures with low data values produce dark pictures on the display while HDR with high data values produce bright pictures. On the other hand, MPEG encoders are designed for Rec. 709 standards that are standards with relative colorimetry, i.e. there is no physical relationship between the data value and the real luminance to be displayed. For these reasons, HDR content with dark scenes produces dark LCD panel data that are inefficiently encoded by MPEG encoders.        